1. Field of the Invention
The present invention relates to data multiplexing apparatuses, methods and systems, and can be applied to, for example, digital video-on-demand systems, and digital transmission systems such as community access television (CATV). The present invention sets scheduling in accordance with reading requests, and transmits data streams obtained by multiplexing materials (hereinafter referred to as xe2x80x9cclipsxe2x80x9d) stored in a server, whereby reducing a load on a host computer used for managing a system of this type.
2. Description of the Related Art
In conventional digital transmission systems such as CATV, with a videocassette recorder (VCR) or the like managed on a time base, video signals output from the VCR or the like are encoded and multiplexed before being transmitted.
In the system of this type, by storing encoded video data in a server before transmitting them, the system structure can be simplified, and time-shifted programs or the like can easily be transmitted. In such a case, conventional apparatuses are combined to constitute a simplified system as shown in FIG. 15.
In a digital transmission system 1, an encoder 2 generates transport streams by using, for example, the standard of the Moving Picture Experts Group (MPEG) 2 to encode clips that are recorded in a server 3, and outputs the transport streams to the server 3.
Under the control of a host personal computer (host PC) 4, the server 3 holds the transport streams output from the encoder 2 in units of packets, and outputs the transport streams in units of packets at a predetermined timing. In other words, the server 3 selectively reads a plurality of programs stored based on the transport streams in accordance with programs to be transmitted from the digital transmission system 1, and outputs clips read based on the transport streams corresponding to the plurality of programs. At this time, the server 3 sets a packet identification (PID), etc., which is instructed by the host PC 4 in the packets of each transport stream, whereby reforming and outputting each transport stream.
A multiplexer (MUX) 5 decomposes the transport streams transmitted from the server 3 into transport stream packets (hereinafter referred to as xe2x80x9cTS packetsxe2x80x9d), and time-divisionally multiplexes the TS packets. At this time, under the control of the host PC 4, the multiplexer 5 time-divisionally multiplexes transport streams (normally, four to six transport streams) for predetermined channels that are assigned to one frequency band obtained by performing frequency multiplexing, whereby outputting multiplexed streams based on a plurality of clips.
Interfaces (I/Fs) 6A to 6N output the multiplexed streams output from the multiplexer 5, to modulators (MODS) 7A to 7N.
The modulators 7A to 7N use, for example, quadrature amplitude modulation (hereinafter referred to as xe2x80x9c64QAMxe2x80x9d) to digitally modulate the multiplexed streams input from the I/Fs 6A to 6N, and output RF signals as modulated results.
A head end (HE) 8 performs frequency multiplexing of the RF signals output from the respective modulators 7A to 7N, and transmits the frequency-multiplex signal to a transmission link such as a coaxial cable.
In each terminal, in accordance with selection by a user, a set-top box (STB) 9 selectively receives the desired RF signal from the frequency-multiplex signal transmitted from the HE 8. The STB 9 demodulates the received RF signal to select the desired transport streams, and demodulates the original video signal, etc., based on the transport streams. Accordingly, in the digital transmission system 1, the desired programs can be viewed on monitors 10, and by transmitting the programs via the server 3, such a simplified structure can enhance usability.
In the case where the server 3 and the multiplexer 5 are independently provided using a combination of conventional devices as described above, as the number of output channels from the server 3 increases, the amount of processing by the multiplexer 5 increases. This increases a load on the host PC 4 managing the server 3 and the multiplexer 5. In addition, the number of devices constituting the entire system increases to complicate the system structure.
Accordingly, it is an object of the present invention to provide a data multiplexing apparatus, a data multiplexing method, and a data multiplexing system in which a load on a host PC can be reduced.
To this end, according to a first aspect of the present invention, the foregoing object has been achieved through provision of a data multiplexing apparatus comprising: scheduling means for generating scheduled data for instructing the reading and multiplexing of clips; reading means for sequentially reading, from storage means containing the clips, transport stream packets based on clips corresponding to the scheduled data; multiplexing means for time-divisionally multiplexing transport stream packets output from the reading means in accordance with the scheduled data; and data transmission means for transmitting data output from the multiplexing means; wherein the transport stream packets read from the storage means, which correspond to a plurality of channels, are time-divisionally multiplexed without being separated into data for the respective channels.
Preferably, the scheduling means updates the scheduled data in accordance with a request input at a predetermined timing.
The data transmission means may include digital modulation means for digitally modulating the data output from the multiplexing means, and outputting the digitally modulated data.
According to a second aspect of the present invention, the foregoing object has been achieved through provision of a data multiplexing method comprising the steps of: generating scheduled data used for instructing the reading and multiplexing of clips; sequentially reading, from storage means containing the clips, transport stream packets based on clips corresponding to the scheduled data; and time-divisionally multiplexing the transport stream packets output from the reading means in accordance with the scheduled data, and transmitting the time-divisionally multiplexed transport stream packets; wherein in the step of time-divisionally multiplexing the transport stream packets output from the reading means, which correspond to a plurality of channels, the transport stream packets are time-divisionally multiplexed without being separated into data for the respective channels.
Preferably, in the data multiplexing method, the scheduled data are updated in accordance with a request input at a predetermined timing.
According to the present invention, by time-sequentially generating scheduled data for instructing the reading and multiplexing of clips in accordance with transmission requests, using the scheduled data to read stored clips, and multiplexing the read clips, unified control of components constituting a system of this type can be performed, whereby a load on a host PC can be reduced. In addition, read transport stream packets are directly multiplexed between corresponding clips, whereby the entire system structure can be simplified.